The present invention relates to antennas and, more specifically to quadrature meanderline loaded antennas.
In the past, efficient antennas have typically required structures with minimum dimensions on the order of a quarter wavelength of the lowest operating frequency. These dimensions allowed the antenna to be excited easily and to be operated at or near resonance, limiting the energy dissipated in impedance losses and maximizing the transmitted energy. However, such antennas tended to be large in size at the resonant wavelength, and especially so at lower frequencies.
In order to address the shortcomings of traditional antenna design and functionality, the meanderline loaded antenna (MLA) was developed. U.S. Pat. Nos. 5,790,080 and 6,313,716 each disclose meanderline loaded antennas. Both of these patents are hereby incorporated by reference in their entirety.
Generally, an MLA (also known as a xe2x80x9cvariable impedance transmission linexe2x80x9d or VITL antenna) is made up of a number of vertical sections and horizontal sections. The vertical and horizontal sections are separated by gaps. Meanderlines are connected between at least one of the vertical and horizontal sections at the corresponding gaps. A meanderline is designed to adjust the electrical (i.e., resonant) length of the antenna, and is made up of alternating high and low impedance sections. By switching lengths of the meanderline in or out of the circuit, time delay and phase adjustment can be accomplished.
In addition, an MLA allows the physical dimensions of antennas to be significantly reduced while maintaining an electrical length that is still a multiple of a quarter wavelength. Antennas and radiating structures built using this design operate in the region where the limitation on their fundamental performance is governed by the Chu-Harrington relation. Meanderline loaded antennas achieve the efficiency limit of the Chu-Harrington relation while allowing the antenna size to be much less than a quarter wavelength at the frequency of operation. Substantial height reductions can be achieved over quarter wave monopole antennas while achieving comparable gain.
Thus, meanderline loaded antennas provide certain benefits over conventional antennas. However, although a switchable meanderline allows the antennas to have a very wide tunable bandwidth, the bandwidth available for simultaneous or instantaneous use is relatively limited. As such, meanderline loaded antennas can be limited for certain applications, such as multi-band or multi-use applications, or those where signals can appear unexpectedly over a wide frequency range. Moreover, the need for wideband or multi-band antennas continues to grow in response to requirements for aperture and volumetric efficiency for antennas used in systems such as wireless and satellite applications (e.g., GPS and cellular telephone platforms).
What is needed, therefore, are meanderline loaded antennas having a wide bandwidth available for simultaneous or instantaneous use.
One embodiment of the present invention provides a quad meanderline loaded antenna adapted to simultaneously provide RHCP, LHCP, and Vpol modes. The antenna includes a first pair of opposed meanderline loaded antennas, and a second pair of opposed meanderline loaded antennas in orthogonal relationship with the first pair of opposed meanderline loaded antennas. A first inverse hybrid is operatively coupled to the first pair of opposed meanderline loaded antennas, and is configured with a xe2x80x9c0xe2x80x9d input/output port and a xe2x80x9c180xe2x80x9d input/output port. A second inverse hybrid is operatively coupled to the second pair of opposed meanderline loaded antennas, and is configured with a xe2x80x9c0xe2x80x9d input/output port and a xe2x80x9c180xe2x80x9d input/output port. A quadrature hybrid is operatively coupled to the xe2x80x9c180xe2x80x9d input/output ports of the first and second inverse hybrids, and is configured with a left-hand circularly polarized (LHCP) signal port and a right-hand circularly polarized (RHCP) signal port. A combiner/splitter is operatively coupled to the xe2x80x9c0xe2x80x9d input/output ports of the first and second inverse hybrids, and is configured with a vertically polarized (Vpol) signal port. With this particular embodiment, an azimuthal angle of arrival associated with the antenna is provided by phase difference between signals at the RHCP and Vpol ports or by phase difference between signals at the LHCP and Vpol ports.
Another embodiment of the present invention provides a quad meanderline loaded antenna adapted to simultaneously provide four independent beams. The antenna includes a first pair of opposed meanderline loaded antennas, and a second pair of opposed meanderline loaded antennas in orthogonal relationship with the first pair of opposed meanderline loaded antennas. A first inverse hybrid is operatively coupled to the first pair of opposed meanderline loaded antennas, and is configured with a xe2x80x9c0xe2x80x9d input/output port and a xe2x80x9c180xe2x80x9d input/output port. A second inverse hybrid is operatively coupled to the second pair of opposed meanderline loaded antennas, and is configured with a xe2x80x9c0xe2x80x9d input/output port and a xe2x80x9c180xe2x80x9d input/output port. A first quadrature hybrid is operatively coupled to the xe2x80x9c0xe2x80x9d input/output port of the first inverse hybrid, and to the xe2x80x9c180xe2x80x9d input/output port of the second inverse hybrid, and is configured with a north signal port and a south signal port. A second quadrature hybrid is operatively coupled to the xe2x80x9c0xe2x80x9d input/output port of the second inverse hybrid, and to the xe2x80x9c180xe2x80x9d input/output port of the first inverse hybrid, and is configured with an east signal port and a west signal port.
Another embodiment of the present invention provides a method for manufacturing a quad meanderline loaded antenna. The method includes providing a first pair of opposed meanderline loaded antennas, and a second pair of opposed meanderline loaded antennas in orthogonal relationship with the first pair of opposed meanderline loaded antennas. The method further includes operatively coupling a first inverse hybrid to the first pair of opposed meanderline loaded antennas, the first inverse hybrid configured with a xe2x80x9c0xe2x80x9d input/output port and a xe2x80x9c180xe2x80x9d input/output port. The method further includes operatively coupling a second inverse hybrid to the second pair of opposed meanderline loaded antennas, the second inverse hybrid configured with a xe2x80x9c0xe2x80x9d input/output port and a xe2x80x9c180xe2x80x9d input/output port. The method further includes operatively coupling a first quadrature hybrid to the xe2x80x9c0xe2x80x9d input/output port of the first inverse hybrid, and to the xe2x80x9c180xe2x80x9d input/output port of the second inverse hybrid, the first quadrature hybrid configured with a north signal port and a south signal port. The method further includes operatively coupling a second quadrature hybrid to the xe2x80x9c0xe2x80x9d input/output port of the second inverse hybrid, and to the xe2x80x9c180xe2x80x9d input/output port of the first inverse hybrid, the second quadrature hybrid configured with an east signal port and a west signal port.
The features and advantages described herein are not all-inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and not to limit the scope of the inventive subject matter.